(1) Field of the Invention
The present invention relates to a noise reducing device for reducing noise radiating from a printer of business equipment which is used in offices of the like.
(2) Related Art Statement
Hitherto, there is a problem of noise radiating from printers of business equipment. It is however impossible to completely shield a sheet supply opening and a sheet delivery opening in the printer in order to prevent noise from radiating out of the printer. Accordingly, it has been required to reduce noise radiating from the sheet delivery opening located near a printing drum of the printer.
A noise reducing device for printer is disclosed in Japanese Patent Application publication Laid-open No. 60-162680 in which a conventional interfering type noise reducing hollow body consisting of a plurality of hollow ducts having different passage lengths is arranged at one side of the sheet delivery opening of the printer. However, the noise reducing device described in the publication is vertically mounted on the upper surface of an outer casing of the printer at one side of the sheet delivery port and arranged such that a printed sheet is guided from the sheet delivery opening over the upper end of the noise reducing hollow body along the noise incident side thereof. Therefore, a portion of noise radiating from the sheet delivery opening enters into the hollow ducts having different passage lengths of the noise reducing device via each of noise incident inlets of the hollow ducts which is opened at the side of the sheet delivering opening. The portion of the noise passes through the hollow ducts and is controlled by the different passage lengths and then radiated from outlets at the radiate side of the noise reducing device with different phases depending on the different passage length. Therefore, the controlled noise radiated from the outlets are interfered to each other to reduce the level of noise. The remainder of noise radiated from the sheet delivery opening passes along the printed sheet without passing into the hollow ducts and is directly propagated over the upper end of the noise reducing device. Such directly propagated noise is also interfered with the controlled noise having different phases at the radiating side of the device to be reduce the level of the noise.
The aforementioned interfering type noise reducing device, however, has disadvantages that the construction is bulky and a part of the directly propagated noise passing along the printed sheet is upwardly propagated and is not effectively interfered with the controlled noise having different phases so that the noise reducing effect is not so sufficient as expected because the noise reducing device is vertically mounted on the upper surface of the printer and the remainder of the noise from the sheet delivery opening is mainly upwardly propagated along the upper surface of the printed sheet which is guided over the upper end of the noise reducing device.